Snap switch for detector mechanism



Jan. 4, 1955 R. A. F. SANDBERG SNAP SWITCH FOR DETECTOR MECHANISM 4 Sheets-Sheet 1 Filed March 25, 1952 N? m a H 5 m n m \LQ N za 0 \I N; ME g g 8 Mm n fii Q 8 1: 5

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Jan. 4, 1955 R. A. F. SANDBERG SNAP SWITCH FOR DETECTOR MECHANISM 4 Sheets-Sheet 2 Filed March 25, 1952 Jan. 4, 1955 R. A. F. SANDBERG sNA SWITCH FOR DETECTOR MECHANISM Filed March 25, 1952 4 Sheets-Sheet 5 Q k 5 a 8 m Ead EF' IHI '-INVENTOR 3 h Rolffll'Sandber Z ATTORNEY Patented Jan. 4, 1955 SNAP SWITCH FOR DETECTOR MECHANISM Rolf A. F. Sandberg, Queens Village, N. Y., assignor to John Volkert Metal Stampings Incorporated, Queens Village, N. Y., a corporation of New York Application March 25, 1952, Serial No. 278,434

12 Claims. (Cl. 200-136) This invention relates to switch units and more particularly to snap switch mechanism for detectors of thermal and like stress detectable changes, and still more particularly to adjustable thermal switch units therefor.

My invention concerns itself with, and it is an object thereof to provide, a snap action switch and a detector unit embodying the same whereby a variety of changed conditions may be automatically detected by the operation of a switch and changes produced thermally or by other stresses may be translated and magnified to produce a snap action controlling the making or breaking of an electrical circuit for signaling the changed condition.

More particularly it is an object of this invention to provide a detector having a snap action switch which may be used thermally to detect variations in temperature, to provide the making and breaking of an electrical circuit rapidly and to prevent arcing and insure longevity of the contacting points, including adjustability of a single device for a wide temperature range, and further characterized by one capable of providing a make and break for a variety of current conditions, including non-inductive loads which shall be stable in an assembly accompanied by vibration, without disrupting the accuracy, including resistance to atmospheric conditions in temperature, humidity, pressure, and without ailecting the sensitivity of the device to provide, in a single installation, a wide range of detector usefulness.

My invention has for its object to provide a mechanical motion for making and breaking the contacts of an electrical circuit by the diiierence in thermal expansion of dissimilar materials under the incidence of the stresses created in dissimilarity of expansion of these different materials.

The expedients known to me for effecting the making and breaking of contacts responsive to thermal stresses fail to supply sensitivity over wide ranges of temperature conditions and require mechanism for amplification of the movement which limits unduly the sensitivity necessary under the conditions which require both speed of movement and sensitivity to variable conditions adjustable over a wide range.

By my invention the transposition of the movement of stresses of elongation of differentially responsive materials, such as materials of diflerential thermal coefficients of expansion, is transmitted to an over-center member for snap action, make and break of contacts which is effected by a shifting movement which makes possible the detection of such elongation stresses over a wide range of conditions with adjustment for sensitivity within pre scribed ranges and extreme compactness.

To attain these objects and such further objects as may appear herein or be hereinafter pointed out, I make reference to the accompanying drawing, forming a part hereof, in which- Figure l is a perspective view showing the snap switch unit;

Figure 2 is a magnified longitudinal sectional view taken on the line 2-2 of Figure 1, applied in position, together with the circuit diagram;

Figure 3 is a magnified section taken on the line 3-3 of Figure 2; v

Figure 4 is a magnified section taken on the line 4-4 of Figure 2;

Figure 5 is a fragmentary magnified section taken on the line 5-5 of Figure 2;

Figure 6 is a magnified fragmentary section taken on the line 6-6 of Figure 2;

Figure 7 is a section taken on the line 7-7 of Figure Figures 8 to 11 are sections taken on the lines 8-8, 9-9, 10-10 and 11-11, respectively, of Figure 7;

Figures 12, 13, 14 and 15 are magnified perspective views of details;

Figure 16 is a partially broken section corresponding to Figure 2 in the break position of the contacts;

Figures 17 and 18 are diagrammatic illustrations of the device;

Figure 19 is a diagrammatic illustration of another embodiment.

Making reference to the drawing, I show a thermal detector unit 10 comprising a terminal casing 11 and a detector casing 12 which are extended to each side of a mounting flange 13. The mounting flange may be supported in contact with a wall 14, having an aperture 15 through which the detector casing may project. The flange 13 is formed with an axial boring 16 through which projects the terminal rod 17. A metallic ring 18 is transversely supported and is formed with an axial seal at the glass seal 19, forming the bond between the terminal and the metal ring. The casing 11 provides an enclosure for the terminal rod 17 and includes an upstanding annulus 20, screw threaded internally and externally, surrounding the seat 21, against which the metal ring 18 is pressed by the sealing screw 22. Nested within the boring 23 of the sealing screw there is a ceramic tubing 24, within which the terminal contact 25 extends in frictional engagement with the end 26 of the terminal rod 17.

The terminal 25 is formed with an hexagonal collar 27 held in non-rotating position in the hexagonal depression of the insulator cap 28 and by ribs 29 entering the slots 30 of the annulus screw 20. A cap nut 31 screw threadedly engages the neck 32 of the annulus 20, there being an inwardly directed flange 33 engaging the shoulder 34 of the insulator cap 28, but separated by an interposed gasket 35 to provide an enclosure for the terminal end of the switch.

The terminal 25 has a screw threaded stud 36, and non-rotatable engagement for this stud is provided by making the collar 27 and the socket 27a of the cap 28 hexagonal. The stud 36 may carry the clamping nuts 36a for the conductor 37, leading to the signaling de- 1 vice 38 of the battery assembly 39 and the ground lead 40. Bolts 41 serve to clamp the flange in engagement with the wall 14, which is grounded by the lead 42.

, Extending from the flange 13 is the conductor casing 12 previously described, which may be made of relatively g. high coefiicient of expansion metal, welded or otherwise sealed at its end 43 in the flange 13. The free end 44 has an internally threaded throat 45 to receive the switch assembly carried by the adjustment seal base 46.

Into the casing 12 there is initially inserted the member comprising a tubing 47 which is made of low coetficient of thermal expansion material, of which fused quartz is an example. Tubing known as Vitreosil comprising a glass of coefficient of thermal expansion n .54 10 per C. may be employed. The ends 43 and 49 are finished by grinding to a correct length, to present an accurate end for contact under pressure which will appear as this description proceeds.

The end 49 serves as the abutment for the ring 50, to which the slide assembly shown in Figures 12 and 13 {E318 connected by welding, there being provided a plurality of spacing springs 51 forming grounding snubbers to axially support the slide assembly, with undulations 52, at spaced points, to increase the resilient support 7 and for purposes of making electrical contact, as will apg pear hereafter as this description proceeds.

The ring 50 has likewise welded to it spaced arms 53, to which the outer slide 54 is attached. The outer slide comprises a substantially rectangular casing 55,

7 having side walls 56 and 57, joined by the webs 58 and 7.59 to leave intermediate open edges 60 from the side walls 56 and 57. Stamped from the side wall 57 there is provided a cross plate 61, to which there is spot Welded at the point 62, the bowed snap spring 63. The leading 80 edge of the casing 55 has a cross web 64, to which the ijjforward end of the snap spring 63 is affixed. The

web 59 has an aperture 66 for accessibility to a welding electrode, for purposes which will appear hereafter.

With this construction there is provided an inner slide 67, shown in detail in Figure 12, which is made of sheet metal and has a cross web 68 extended between the walls 69 and 70. To the cross web 68 there is affixed the contact spring 71 at its end 72 by a weld. The forward end of the inner slide 67 has a cross finger 73, to which the snap spring 74 is attached, to lie beneath the lower surface of the cross finger 73. Webs 75 and 76 outline shoulders 77 and 78. Edges 79 and 80 provide a longitudinal slot, permitting the nesting of the outer casing 55 and the inner casing 67 telescopically, and to position the bowed snap spring 63 with its end 65 slidable beneath the short spring 74.

With the ends of the bowed spring 63 substantially co-terminously positioned and aligned as shown in Figure 16, the short spring 74 is welded to the bowed snap spring 73 at the point 74a by a welding electrode through the aperture 66. In this position the rear end of the bowed spring 63 is welded through the aperture 31, to provide a spot weld 02 between the rear portion of the bowed spring 63 and the contact spring 71.

The location of the spot welds 74a and 82 provides a coupling wherein the snap spring 74 may move relatively to the end 65 of the bowed snap spring 63, though integrated by the spot weld 74a. Likewise, the cross webs 61 and 68, carrying the ends 63a and 72 of the bowed snap spring and contact spring by independent spot welds 62 and 66:: may move relatively to each other with regard to the spot weld 82 joining the contact spring '71, which spot weld 82 is applicable through the aperture 32a.

In the nested arrangement there is then positioned the yoke 83, whose ends 84, 85 extend through the slots 86, 87, into the anchor holes 88 and 89 of the walls 56 and An expansion spring 90 is centered on the yoke 83 to engage the finger 83a at one end and to engage a plate 91 at the other end. The plate 91 presses against the webs 75 and 76 of the shoulders 77 and 73 of the inside slide 67, thereby moving the slides 54 and 67 with relation to each other and bowing the bowed snap spring 63 in the position shown in Figures 2 and 7. The effect is to have the segment of the bowed spring 63 between the spottings 74a and 82 pushed by the segment 74 at its remote end and pulled by the cross plate 68 at the opposite inner end. In this adjusted position the contact spring 71 has its end 93 formed with a contact 94, provid ing a highly magnified movement past the center line C. The assembly of contacts carried by the ring 50 may then be inserted within the tubing 47 to abut the edge 49 and to compress the springs 51 so that the undulations 52 center the assembly axially.

in this condition the adjustment and seal assembly shown in magnified detail in Figures and 15 is screwed into position forming a pressure tight seal at 44. This comprises an adjustable seal base 46, previously mentioned, having a neck 95 to which is affixed a bellows 96, to engage a cap assembly 97. The cap has a tubular neck through which extends an adjustable extension rod 99. The over-travel spring 100 is biased under compression between the collar 101 and the shoulder 102 of the sleeve portion of the adjustable seal cap 97. An anchoring pin 103 extends through the rod 99 in the boring 104, to hold the extension rod 99 under tension with relation to the sleeve 97. A nose 105 may be extended into the socket outlined by the inner slide 67 between the straps 75 and 76 to bring the collar 101 in close contiguous relation to the edge 106 but normally not contacting the same until the adjustments hereinafter to be described are effected.

The adjustable seal cap 97 has a screw threaded stem 107 engaged by the temperature setting screw 168, whose neck 109 is screw threaded within the boring 110. The end of the temperature setting screw 100 is provided with a wrench engaging slot 111, such, for example, as a spanner wrench or Allen wrench, whereby, in view of the threaded relationship of the stem 107 to the socket 110, a differential adjustment of the two screws of the adjustable seal cap may be secured with relation to the detector casing 12 in the threaded throat 45. After desired adjustment for temperature range, etc., is made,

, locking set screw 107a is set in place to insure that the setting is maintained. After such adjustments have been completed, the cap 112a is screwed or otherwise affixed in position.

Feeding of the adjustable seal cap by turning the screw 108 will contact the collar 101 against the edge 106 and will overcome the expansive action of the spring to move the inner casing 67 relatively to the outer casing 54 and position the bowed snap spring 63 to the position shown in Figure 16 and space the contact 94 from the terminal 17.

From the construction described it will be observed that the over-center bowed snap spring 63, in carrying the contact spring 71 with relation to the terminal rod 17, serves to magnify any movement eccentric to the axial line through the apparatus on which the terminal rod 17 and the ends of the bowed snap spring 63 lie. The relative movement of the casings 55 and 67 transmits push-pull forces to the over-center spring 63 without any lateral yielding, tending to bow the spring 63 accurately in an over-center position, with a turning movement, which, upuon compression, bows the over-center spring upwardly in that the cross web 68 moves the weld point 82 about the weld point 62 as a center, and positiveness of action is assured by the pulling action of the snap spring 74 with relation to the weld 74a about the forward end 65 on the cross web 64.

By the use of the spring loading or biasing action of the expansion spring 90, the casings 55 and 67, acting on the yoke 83, and the plate 91, are normally held in a position bringing the terminal ends of the bowed snap spring 63 to close the contact between the contact 94 and the terminal rod 17, closing the electrical circuit through the signal light 38 previously described. Where it is desired to use the switch assembly 12 to indicate a change in condition from a relatively low temperature to an increased temperature by the expansion occurring with relation to the low coefficient of expansion material 47, and the relatively high coefiicient of expansion detector casing 12, the expansive action of the spring loading or biasing member 90 is overcome for setting the same by feeding the nose 1 35 into engagement with the edge 106 under the influence of the adjustment assembly shown in Figure 5 wherein the nose 1135 may be moved by reason the sealed flexibility of the bellows 96. The adjustment on the stem 107 to obtain a greater biasing or spring loading pressure in effect provides an accumulated yielding pressure which must be dissipated with the expansion of the detector casing, which carries with it at one end the adjustment seal base 46 before the weaker expansion spring 90 becomes effective when the flange 101 withdraws from the edge 106 sufliciently. Hence, the longitudinal relative movement with a compressive and pulling force on the over-center spring, as occasioned by the relative movement of the casing 12 and tubing 47, is availed to amplify minute movement. The weaker expansion spring 90 throws the over-center spring 63 in one direction from the axial position. The nose 105, whether resiliently urged or by a solid member, in effect cocks this spring and positions the over-center spring in the opposite direction. The accumulated spring pressure in spring 90 is released for snap action switching upon the expansion of the easingto remove the nose 105 from engagement with the edge 106 to the position before loading of the spring 100.

Thus it will be noted that while there has been included adjusting means acting against the edge 10.6,, which is variable to the degree that the spring is loaded, giving a very wide range of detection features,

it is contemplated by me to employ a feed for the nose which fixedly presses the collar 101 thereof against the edge 106, where a low range of detecting conditions is found satisfactory, such, for example, as in a thermostatic control regulating home temperature conditions.

By reference to Figures 17 and 18, the advantages of my invention will become more apparent in the diagrammatic representation of the assembly. The section of the member A between the points 74a and 82 may be considered as the main over-center snap spring 63 with pivot points at the points which correspond to the welds 74a and 82. In accordance with the parts as described which represent a predetermined setting thereof, the relative movement of the casings causes the points 74a and 82 to be pushed and pulled from the axial position in that the section A is fastened to the abutments 64 and 61 on the slide 55 which, by reason of the normal length of the member 63 from the points 65 and 64 being greater than the distance between the abutments, bows the spring 63 in a non-axial position. It is clear, too, that the over-center spring 63 may be at rest in either position under compression. Members 74 and 72 are welded to abutments 73 and 68, respectively, of the slide 67 and subsequently members 74 and 71 are joined to member 63 at points 74a and 82. Under such stresses as the slides 55 and 67 may be subjected, the strip 63 may come at rest in one of two bowed positions nonaxially. The addition of the spring 90 will tend to direct the arm corresponding to the contact spring 71 into contacting position biased against the terminal rod 17, as contrasted with the vibration dampened condition when the spring 71 engages the abutment 64 as shown in Figures 16 and 17. If a casing 12 anchors an adjusting plug or a spring 100 to press against the collar 101 and the slide 54 is restrained by a ring 50 against the tube 47 at its end 49 by reason of greater preloading action of the adjusting means with or without the spring 100 than the expansive force in the spring 90, the strip A corresponding to the spring 63 will be deflected from the position due to the spring 90 as shown in Figure 17, to break the contact. The distance X is representative of the effective distance which collar 101 must move to allow spring 90 to move the slide 67. The amplification which may be obtained at the distance X is a factor of the relative change in elongation of the detector casing 12 and the low coefficient of expansion member 47 serving as an abutment or stop to the movement of the slide 55.

A graphic indication of the sensitivity of the device due to the stresses to which the detector casing 12 may be subjected as by thermal changes is evident from the following:

If the angle of the tangent to the member 63 at either point 74:: or 82 is d to axis C, the distance along the arc of the center line of the member 71 from 61 to 82 may be representative of a and from 73 to 82 along the arc of the part of the member 63 which is located here is a" and the thickness of the material of the strips is 1. There is then obtained the distance which the slide 67 must travel to rotate the point 82 from the position shown in Figure 17 to the center line or axial line by the following equation:

For a relative displacement which will result in an angular change in the strip 63 of 5 and given a thickness for the strip of .005", the distance may be calculated for the relative movement of the slides 55 and 67 to provide the following:

a- Xt Thus it will be seen that by actual calculation a relasin 56:0057

distance:

This shows that the lever arm for mechanism providing transverse movement would require a distance more than ten times that effected by the aonaratus in accordance with this invention and without any amplification at the point where the moment of force is applied.

It will be observed that the element of adjustment as provided by the adjustable seal serves to preset the mechanism. The operating point is controlled by the location of the adjustable assembly which determines the distance the casing 12 must expand to release the pressure plate 91 so that the spring 90 is free to act and defiect the over-center strip to make position.

I do not intend to be bound by the illustration of sizes and proportions and modification may be made to suit the circumstances which may be encountered.

Likewise, the over-center spring strip or the constitution of this material plays no important part in the operativeness or sensitivity of the device as it is the relative motion between the slides which controls the position of the over-center bowed springstrip and accordingly, nov

special attention or tempering treatment need be given to the relatively movable parts or for the selection of the kind of material of which the slides and the spring strips are made.

Other features of the invention involved in the adjustment of the biasing spring relate to the adaptability by adjustment to an over-range protection-for example, if the device is used to detect thermal changes in temperate or tropical localites, it is important that the same instrument be adaptable for use where the mean temperatures may drop to those experienced in arctic locations, with normal temperatures well below sub-zero. The resiliency of the biasing member for the storing of the accumulated energy makes the device adaptable without destruction or undue strain over a wide range of operating conditions with accuracy.

Still other features of my invention will be apparent from the construction described in that the relative linear changes of the detector or sensing casing are transmittted without magnification or large dimensional linkage to the over-center spring so that these relatively microscopic linear changes are transmitted by movement in parallelism to the over-center strip, to provide quick acting make and break contact.

Thus, by my construction, in view of the minute nature of the masses involved in the linkage mechanism for transmission of the relative linear changes, effects of vibration are minimized and lost motion due to extensive linkage or bearing points are eliminated. Positiveness of action due to elimination of any lost motion is likewise secured, with snap action make and break contact.

It will also be observed that by my construction a completely sealed unit is made possible, eliminating the likelihood of deterioration by changes in atmospheric conditions and responsiveness for making and breaking action is possible over a wide range of electrical energy across the contacts.

While I have shown a complete combination which provides the preferred installation, it will be understood that isolated elements disclosed may have utility independly of the entire assembly, and, accordingly, my invention is not to be limited by reason of the entire as-' sembly which may be disclosed.

In Figure l9 1 have illustrated another embodiment of my invention in which an inversion of operation is.

established. The cooperating parts and spring loading by presetting is effected by a pulling force rather than the adjustment described which exerts a pushing force. Thus, in the prior described embodiments, the contact 71 makes contact upon expansion of the sensing tube 12 by releasing the accumulated spring pressure 90. However,

in the embodiment shown in Figure 19, the contact 71 is normally open and makes contact by pulling member 68b. For this purpose, the over-center strip assembly has the strip 63 thereof spot welded on the relatively fixed anchors 61a and the opposed end 64 (not shown in Figure 19) so that the over-center strip 63 is bowed. The spring a is compressed and biased normally to bring the strip 63 to its uppermost position and to bring the contact 71 away from terminal rod 17 engaging position by pushing the slide 68b. Pie-setting is effected by varying the gap b tween 104a and 103a through the moving of adjustable plug 912:: which is fixed relatively to move with the sensing case As the adjustment is made to pre-set the device for operation at a higher temperature by moving adjustable plug 97:: in a direction opposite to the expanding direction of sensing casing 12, spring 100a is compressed so that the head 103a of stem 113 moves relatively to the dotted position within the socket of the plug 97a which is provided with adequate clearance. The distance between the pressure face of the head 103a and the shoulders 1041: represents the pre-setting distance which the sensing tube 12 must move or expand by thermal changes before shoulders 104a contact the head 103a of the stem 113 and pull abutment 68b until it snaps the over-center spring 63 from the upward bowed position to the contacting position, which was the normal position of the over-center spring 63 for this embodiment.

In the last described embodiment it will be observed that as the pre-set temperature point of contact is passed by the continued expansion of the sensing tube 12 due to continuing rise of temperature, the entire assembly is drawn out of the low coeflicient of expansion member 47 by the engagement with the head 103a. However, the

first embodiment carries the nose 105 and collar 101 as a separable element.

It will thus be observed that in both forms of mech anism the over-center spring 63 and its anchoring means and inner and outer slide members form an independent assembly. Thus, the sensing tube or the element which expands and is subjected to continued reactive forces producing the motion, has no disruptive or damaging influence on such assembly. Any accidental over-range condition will still leave the mechanism intact and free from the permanent influence of the accidental over-range condition.

It will be understood that while I have illustrated my invention with regard to securing snap action or an overcenter spring by the transmission of the motion of a stress sensing element in a push-pull transmission in a plane in parallelism or substantially tangential to the over-center strip at opposite ends of the strip, anchored at opposite ends in a non-axial position, it will be understood that such push-pull action may be exercised to one side of said strip.

It Will also be understood that while "i have illustrated my invention as having value when all of the features do scribed are used in their entire assembly, do not intend to be restricted thereto and that my invention is considered to comprise meritorious features with regard to various elements thereof which may be employed in other combinations upon their features having een supplied and disclosed.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. A snap-action switch having a pair of contact menu bers and mounted upon a stress detector member com prising an over-center spring biased strip carrying one contact member extended therefrom on arm for magnified make and break movement in relation to the other contact member, a second strip closely positioned thereto, said second strip being joined adjacent the over-center portion of the first strip, and with other portions free to move relatively to each other and having means to bias the joined ends in one direction, the free ends of the strips being carried on anchoring means free to shift in relation to each other in planes substantially tangential t the ovcr-center portion of the first strip, said anchoring means being connected to relatively slidable members engaging said stress detector member e ch different stress responsive factors whereby stresses incident to differential expansion may warp the contact member into make or break positions.

2. A snap-action switch having a pair of contact members and mounted upon a stress detector member comprising an over-center spring strip carrying one contact member extended therefrom on an arm for magnified make and break movement in relation to the other contact member, a second strip closely positioned thereto, said second strip being joined adjacent the over-center portion of the first strip, and with other portions free to move lengthwise relatively to each other having means to bias the joined ends in one direction, the free ends of the strips be"1g carried on anchoring mean i to shift the relation to each ot er in places sub ntially tangential to the over-center portion of the first strip, said anchoring means being connected to relatively slidable members engaging said stress detector member and each having dillerent thermal coefficients of expansion whereby stresses incident to differential expansion may Warp the contact member into make or break positions.

3. In a stres-sensing device comprising those induced by thermal changes having at least a pair of ditterentially responsive elements relatively longitudinally movable under the action of said stress having a terminal member for connection to an electrical circuit, of a snap action switch therefrom responsive to said differential movement in a plane substantially in parallelism to the same, and including an over-center strip having accumulating energy spring biasing means effective under direct linear and substantially parallel movement to said differential members and transmitting substantially push and pull deflection to said over-center strip linearly equivalent to said differential movement comprising a slide having a pair of flexible actuating strips lying in substantial parallelism to each of the opposite sides of said over-center strip, and having each of their adjacent ends connected 8 to said over-center strip, a contact member carried by said strip for make and break engagement with said terminal member with magnified movement.

4. in a stress-sensing device of the character described comprising those stresses inducing elongation changes 1ncluding a first sensing casing member and a second sens ing member less responsive to stresses to which the first member may be subjected whereby the members may shift along their lengths in relatively parallel planes, a stress accumulating member anchored endwise and in parallelism to the direction of shifting of said members connected to and under the influence of said members, to edgewise stress an over-center strip, a biasing member connected to the ends of said strip to overcome the energy accumulating member adjustably connected to the first member within limits to release the stress accumulating member to warp the strip in an oppositely directed position, all of the biasing forces operating in parallelism.

5. In a stress-sensing device comprising those induced by thermal changes whereby over-heat changes may be detected comprising, in combination, a sensing casing member insulated from a terminal rod member electrically, a second casing member having less responsiveness to said stresses for effecting dilterential changes, slidably mounted with relation to each other in parallelism along their lengths, a contact spring within said casing members to make and break a circuit with re spect to said terminal, an over-center spring supported with its ends in parallelism with the path in which said members slide and carrying said contact spring to and from make and break position with said terminal rod member, inner and outer slide members each having means to anchor the opposite ends of an over'cente strip in one direction and an adjustment assembly having spring biasing means connected to opposite sides of said strip and under the influence of the first sensing mem her and movable with said members to deflect said overcenter strip by a stress contra to said first biasing force, said connecting means comprising a flexible strip lying in and being active substantially tangential to the arched over-center spring.

6. A snap action switch having a contact actuated by an over-center strip, the opposite ends or which are anchored in an over-central position to how the same in a fixed direction on a slide therefor, vith freedom of movement to either disaligned position by motion to ward the critical central line, the combination therewith of motion transmitting means connected with said slide having a pair of actuating strips lying to each of the opposite sides of said slide and having each of their adjacent ends connected to the strip first described with their opposed ends anchored on another slide and eilectivc in a plane substantially in parallelism to the plane of the anchors for the strip for transmitting flexible pushing motion on one side of the strip and pulling motion on the other side of the strip.

7. A snap action switch having a contact actuated by an over-center strip, the opposite ends of which are anchored in an over-central position to bow the same in a fixed direction on a slide therefor, with freedom of movement to either disaligned position by motion toward the critical central line, the combination therewith of motion transmitting means connected with said slide and carrying a pair of flexible strips to each of the opposite sides of said slide and having each of their adjacent ends connected to opposite sides of the strip with their remote ends connected to the slide to push and pull the strip and effective substantially in a plane tangential to the strip by movement of the slide relatively to the over-center strip.

8. A snap action switch having a contact actuated by an over-center strip, the opposite ends of which are confined by a slidable anchor member to bow the same in a disaligned position, with freedom of movement to either disaligned central position, the combination therewith of motion transmitting means adjacent the opposite ends of said strip and effecting push-pull movement to opposite faces of said strip by relative movement substantially in the plane of said strip and means for bowing the strip comprising spring loading means and slide means to we set said loading means to how the strip in the oppositely disaligned position whereby release of said pro-setting slide means will snap the strip oppositely.

9. A snap action switch having a contact actuated by s an over-center strip, the opposite ends of which are anchored on a slide and confined to bow the same in a disaligned over-center position, with freedom of movement to either disaligned central position, the combination therewith of motion transmitting means comprising a slide having a pair of flexible strip elements adjacent the opposite ends of said over-center strip, one of said pair lying to each side of said over-center strip effecting push-pull movement to opposite faces of said strip substantially in the plane of said over-center strip and means for bowing the over-center strips comprising spring loading means and adjustable means to pre-set said loading means to how the strip in the opposite disaligned position whereby release of said pre-setting means will snap the strip oppositely.

10. A snap action switch comprising a detector memher, a first slidable member carried thereby and subject to the variations in stresses to which the detector member may be subjected, anchor means on said slidable member, an over-center spring strip anchored adacent each end and on opposite sides thereof to the said anchor means on said slidable member, said strip being permanently bowed to be at rest on either side of its center line, a second slidable member, secondary strips each joined to said second slidable member at their remote ends lying substantially in the same plane as said strip and on opposite sides thereof and connected at each adjacent end to said strip, one of said secondary strips having an extended member movable upon movement of the strip with magnified movement, a contact at the end of said extended member and a second contact in relation to which said first contact is complementary for make and break connection, said slidable members being connected for movement relatively to said detector member whereby stresses applied thereto may warp the over-center strip and move a contact into make or break position by the said snap action.

11. A snap action switch in accordance with claim 10 wherein the bowed condition of said over-center spring strip is effected by spring loading means and resilient pressure means whereby pro-setting of said bowed strip is effected and whereby movement of the detector member will snap the over-center spring strip in an oppositely bowed position.

12. A snap action switch in accordance with claim 10 wherein the bowed condition of said over-center spring strip is eifected by spring loading means, and differential, screw-adjustable resilient pressure means whereby presetting of said bowed strip is effected and whereby movement of the detector member will snap the over-center spring strip in an oppositely bowed position.

References Cited in the file of this patent UNITED STATES PATENTS 1,676,155 Pfiefer July 3, 1928 1,772,002 Harper Aug. 5, 1930 2,185,436 Gordon, Jr Jan. 2, 1940 2,257,990 Turenne Oct. 7, 1941 2,388,712 Schmidinger Nov. 13, 1945 2,441,725 Smith May 18, 1948 2,475,376 Darling July 5, 1949 2,599,437 Dickson June 3, 1952 2,619,567 Walbridge Nov. 25, 1952 

